Internal combustion engines generate drive torque from the combustion of an air and fuel mixture. The combustion process generates exhaust gas that is exhausted from the internal combustion engine to the atmosphere. The exhaust gas contains combustion by-products, such nitrogen oxides (NOx), which may be treated by an exhaust gas aftertreatment system before being released to the atmosphere.
In an exemplary exhaust gas aftertreatment system, a dosing system injects a reductant (e.g. a water solution of urea) into the exhaust gas upstream of a selective catalytic reduction (SCR) catalyst. The reductant breaks down to form ammonia (NH3) that is stored in the SCR catalyst. Ammonia stored in the SCR catalyst reacts with NOx to form diatomic nitrogen (N2) and water, which reduces the NOx levels released to the atmosphere.
In order to minimize the emissions ensuring the maximum efficiency in NOx conversion and, at the same time, the minimum consumption and the minimum release of reductant from the SCR system to the atmosphere, a need exists of improving the control of the dose of reductant injected into the exhaust gas stream upstream of the SCR system.